The present invention relates to a broadband communication device. More particularly, the present invention provides a Si-waveguide-based broadband polarization beam rotator with low loss and high extinction ratio for polarization-independent silicon photonics communication systems.
Over the last few decades, the use of broadband communication networks exploded. In the early days Internet, popular applications were limited to emails, bulletin board, and mostly informational and text-based web page surfing, and the amount of data transferred was usually relatively small. Today, Internet and mobile applications demand a huge amount of bandwidth for transferring photo, video, music, and other multimedia files. For example, a social network like Facebook processes more than 500 TB of data daily. With such high demands on data and data transfer, existing data communication systems need to be improved to address these needs.
Silicon photonics has become very popular for these applications because of the potential to combine high performance with low-cost fabrication. In addition, polarization multiplexing is another attractive, low-cost, and simple way to increase transmission capacity. Polarization beam rotator is a key element for polarization management in next generation polarization-independent silicon photonics circuits. A polarization beam rotator preferred for photonic integrated circuits (PICs) should simultaneously have features like compact size, high extinction ratio, low insertion loss, broadband range, stability, simple structure and high tolerances in manufacture. Conventional polarization beam rotator is either wavelength sensitive (not suit for broadband operation) or based on prism (hard to be made in super compact size). Most recent development of ultra-compact polarization beam rotator is relied on polarization diversity utilizing the large birefringence (˜10−1) of silicon-on-insulator (SOI) nanowire-like waveguide. However, these designs mostly are based on asymmetric waveguides, directional coupler, and slot waveguides, which are all very tolerance sensitive, requiring certain critical dimensions (width or gap) of the waveguides to be smaller than 0.1 μm, and not realistic for process control and will result in very low yield in large scale manufacture. The symmetrical directional coupler is sensitive to fabrication variation. The asymmetrical directional coupler is even more sensitive on the dimension control than symmetrical directional coupler.
Therefore, it is desired to develop improved compact polarization beam rotator that is highly tolerable to waveguide dimension or overlay mismatch, wavelength insensitive, for example across entire C-band window, and temperature insensitive for the integrated silicon photonics circuits.